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Topic: Lewis acids/bases - nucleophiles/electrophiles  (Read 19597 times)

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Offline l_johan_k

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Lewis acids/bases - nucleophiles/electrophiles
« on: May 03, 2009, 06:30:42 AM »
What is the difference between a Lewis acid (base) and a nucleophile (electrophile)?

Offline BluRay

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Re: Lewis acids/bases - nucleophiles/electrophiles
« Reply #1 on: May 03, 2009, 08:47:02 AM »
What is the difference between a Lewis acid (base) and a nucleophile (electrophile)?
The essential difference is that the acidity/basicity is a thermodynamical property, measured with the equilibrium constant, while the electrophilicity/nucleophilicity is a cinetic property, measured with the kinetic constant. So, a strong lewis acid, for ex., can react slowly with a lewis base and so be a weak electrophile; or a strong electrophile, which reacts fast with a nucleophile, can have a low equilibrium constant and so be a weak lewis acid. Usually a strong lewis acid/base is also a strong electrophile/nucleophile, but it's not always so, for the reason I've written.

Offline urvashi314

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Re: Lewis acids/bases - nucleophiles/electrophiles
« Reply #2 on: May 03, 2009, 09:42:41 AM »
lewis acid necessarily accept lone pairs (if you check the definition) and lewis bases donate lone pairs. But electrophilic and nucleophilic species can have either structural lone pairs or charge (which is positive in case of electrphiles and negative in case of nucleophiles). I am not aware of the thermodynamic and/or kinetic reasons  :(

Offline l_johan_k

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Re: Lewis acids/bases - nucleophiles/electrophiles
« Reply #3 on: May 03, 2009, 12:42:18 PM »
H + F > H-F

How would one describe the reaction above in terms of Lewis acid/basic and nucleophilic/electrophilic? (Both H and F are electron-deficient radicals)

Offline BluRay

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Re: Lewis acids/bases - nucleophiles/electrophiles
« Reply #4 on: May 03, 2009, 02:46:30 PM »
H + F > H-F

How would one describe the reaction above in terms of Lewis acid/basic and nucleophilic/electrophilic? (Both H and F are electron-deficient radicals)
In no way because that is not an acide/base reaction. You could even have written H + H --> H2.
A nucleophile is a Lewis base and an electrophile is a Lewis acid; Lewis acid means a species which can accept a lone pair from another species and Lewis base means a species which have a lone pair available to form a covalent bond with a Lewis acid, and in your example there aren't such species.

Even if a nucleophile is a Lewis base and an electrophile is a Lewis acid, nucleophilicity/electrophilicity  don't correspond to basicity/acidity for the reasons in my previous post.

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